FEATURES AND WATER RIGHTS OF YUBA RIVER. 117 



conducted in the deposits left in the beds of the earlier sti'eams. Some of the 

 materials left in the early channels were also subjected to Glacial erosion and trans- 

 portation. These processes doubly concentrated the gold in the original strata and 

 made lines of Glacial flow and modern streams particularlj- rich just below their 

 intersections with the early rivers. 



There have been, therefore, three sets of topographical features: 



First, the earlier topography, established by the upheaval and partial denudation 

 of the range. 



Second, that established by the lava outburst and succeeding erosion. 



Third, that produced by Glacial and post-Glacial erosion, which is cross cai'ved 

 and cut into the preceding systems. In some instances one of these systems remains 

 intact, in others two appear, whilst in rare instances remnants of the earlier systems 

 make up parts of the features now found. 



The combinations of these topographical types are found at the head of Bear 

 River. This river heads 17 miles west of the summit of the Sierras, the headwaters 

 of the North Fork of American River and those of the South Fork of Yuba River 

 reaching beyond those of Bear River to the summit of Mount Lincoln. 



The upper one-third of the drainage basin of the South Yuba was the gathering 

 ground for a glacier. This glacier, instead of following the channel of that river 

 through thettortuous, deep, and narrow channel which turns northwest through 110 

 degrees, plowed its way in a direct course through the lava ridge and eroded Bear 

 Valley, in which Bear -River heads. 



Upon the disappearance of the ice age, Yuba River took the northerly course 

 along a deeply eroded channel, leaving a portion of its Glacial channel below this 

 bend for Bear River. This river therefore occupies a channel far larger than its 

 feeble forces could have excavated. The topography in this region consists of three 

 types. Yuba River below the bend probably occupies a very old channel. The 

 remnants of the mud-lava overflow form the ridges on either side of the Glacial gap 

 at the head of Bear River, whilst this gap and the headwaters of the South Yuba 

 were shaped bj' Cilacial action. 



The glacial gap eroded through the lava ridge is only a few hundred feet above 

 the present bed of the canyon of the South Fork, and affords an easy line for the 

 diversion of its waters into the basin of Bear River, down both sides of which are 

 important ditches. 



The middle and upper portions of the watersheds of the three forks are materially 

 different. The North Fork rises in lavas which vary much in composition and hard- 

 ness, but which generally afford a deep soil for timber and shrub growth. The 

 Middle Fork rises in similar lavas and in granite. The mean elevation of the crest 

 of the Sierras at the head of these forks is about 8,200 feet. The main and tributary 

 streams fall rapidly, and their canyons head well up into the mountains. The sides 

 of these canyons are covered with timber and brush, which, with the deep soil, retain 

 the moistui'e for numerous perennial springs. This is particularl}' the case with the 

 North Fork, making it a reliable and constant stream. The mean annual precipita- 

 tion upon these watersheds is about 54: inches of snow and rain. Warm rains on soft 

 snow sometimes give a high flood run off, but snow remains on the higher peaks 

 until midsummer. Reservoir areas are not numerous, and will be mentioned later. 



